Valves for use with vacuum equipment are essentially different from valves used in conventional systems whose objective is to control the flow of a liquid or gas. In such conventional systems, some leakage of the liquid or gas can usually be tolerated. In the case of vacuum valves, however, even the slightest leak involves not only the loss of a liquid or gas, but total destruction of the vacuum in the vacuum equipment controlled thereby.
The valve of the present invention is intended primarily for use as a vacuum valve in which even the smallest leaks cannot be tolerated. A positive sealing action is assured in the assembly of the present invention when the valve is closed, this being achieved by the use of a Teflon plug which engages a seat in the valve in a leak-free sealing relationship. As described briefly above, the Teflon plug is forced against the seat by the stem of the valve when the valve is closed, and a compression spring also engages the plug, so that it is held in its sealed condition, even in the presence of cold flow of the plastic material.